This invention relates in general to land vehicles and more particularly, to personal mobility vehicles. Most particularly, the invention relates to wheelchairs having camber tubes for supporting manually driven wheels.
Manual, or non-powered, wheelchairs typically comprise a seating surface, a backrest, and a wheelchair frame that is supported by rear wheels, and front casters. Wheelchairs often incorporate a number of adjustments that allow the wheelchair to be customized to fit a particular user size. Typically, manual wheelchairs provide a height adjustment in the rear wheels and/or the front casters. The rear wheels of the wheelchair may be cambered, or angled, with respect to a vertical plane. A wheelchair with a large camber angle has more responsive turning, which is beneficial in sports applications. A wheelchair with little to no camber angle has a smaller overall width and thus greater maneuverability in tight confines.
When an adjustment is made to the rear wheel height or front caster height on a wheelchair with cambered wheels, the rear wheels will toe-in or toe-out. That is to say, the rear wheels become misaligned with respect to horizontal. This misalignment is undesirable because it increases rolling friction. If the rear wheels are raised or the front casters are lowered, the rear wheels will toe-in. Conversely, if the rear wheels are lowered or the front casters are raised, the rear wheels will toe-out. This occurs because the axis of the camber is no longer aligned horizontally. To correct this misalignment the camber tube must be rotated about its axis in order to re-align the camber angle with respect to horizontal. Typically, a horizontal or vertical reference plane is provided on the camber tube to indicate when the camber angle is aligned horizontally. When a horizontal reference plane is provided, a user would hold a bubble level on this surface and rotate the camber tube until the plane is level. When a vertical reference plane is provided, a user would hold a 90-degree angle between the reference plane and the ground and rotate the camber tube until the plane is vertical. Such an adjustment is difficult because it requires additional tools and several hands to perform the operation. U.S. Pat. No. 4,852,899 discloses the use of a spirit or bubble level that is permanently mounted to the top of a camber tube. This invention facilitates toe-in and toe-out adjustment, wherein the user rotates the camber tube until the bubble level is centered. However, because the bubble level is on top of the camber tube, the seating surface blocks the user's view of the bubble level. This makes the invention awkward to use, particularly when the camber tube is situated very close to the seating surface.
What is needed is a camber tube level indicator that can be viewed easily from the side of the wheelchair or from below.